Conventionally, intelligent transport systems (ITS) which utilize information communication techniques to solve transport problems have been increasingly developed. In this field, for example, a technique has been practically used in which the surrounding environment of an automobile (for example other automobiles, pedestrians, obstructing objects and the like around an automobile) is detected by use of sensors, and safety support operations (for example, warning, brake control and the like) for avoiding unsafe situations or reducing the degree of the unsafe situations are performed based on the detection result.
Radars which use millimeter waves having wavelengths of 1 to 10 mm (frequency: 30 to 300 GHz) (so-called millimeter-wave radar) are publicly known as such sensors. Millimeter-wave radars use radio waves, and are advantageous in ensuring a certain degree of sensitivity even under adverse weather such as rain or fog. Millimeter-wave radars transmit a transmission signal (radio wave) to the surrounding regions of the automobile, and receive and analyze a reflection signal (reflection wave) reflected by a detection target object (hereinafter referred to as “target object”) to thereby acquire information relating to the surrounding environment (such as the relative speed and the position (distance, orientation) of the target object).
Millimeter wave sensors have been spread mainly as sensors for vehicle detection for the purpose of avoiding automobile accidents. Further, in recent years, for the purpose of separately detecting artificial objects such as automobiles and pedestrians (human), high-resolution millimeter wave radars using wide-band millimeter wave of 79 GHz band (77 to 81 GHz) have been practically used. For example, PTLS 1 and 2 disclose a technique in which whether a human or not is determined by utilizing the difference (such as dispersion and standard deviation) of the reception power of the reflection signal.